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Neon transformer/shunts (was Re: Danger, and I don't understand why.)
> << Interesting speculations! However, NST's are actually wound with many
> turns of fine copper magnet wire, an this alone accounts for the
> comparatively large resistance of an NST secondary. The current limiting
> behavior in an NST actually comes primarily from the addition of
> magnetic "shunts". These bypass a portion of magnetic flux that would
> otherwise link the primary and secondary windings. This results in a
> substantial increase in the transformer's leakage inductance - and its
> external behavior is similar to connecting an ideal transformer in
> series with a very large inductor.
> >>
> Bert,
>
> That's an excellent explanation of how a transformer is current limited.
Why don't the
> textbook writers use so simple an analogy of a "perfect transformer" in
series with
> an inductance. I have never dissected a NST. Physically, where are the
magnetic shunts
> placed in the xformer? Is the flux shorted out and converted into Eddy
currents? How is
> this calculated?
>
Actually, the ideal transformer and series inductance IS how most textbooks
approach it, at least the ones I have.
There are typically 3 windings on a NST, arranged on a core shaped like a
rectangle. There are two HV windings on either side of the primary LV
winding. The HV windings are connected in series, with the center
grounded. The usual scheme is:
core core core HV core core LV core core HV core core core
core shunt shunt
core
core core core core core core core core core core core core core
Think of magnetic flux flowing around the core through all the windings....
The shunt provides a "bypass" path for some of the flux to go through just
one winding (i.e. leakage).
Does someone have pictures (on the web) of NST innards, showing the shunts?